In drilling for crude oil, natural gas, civil engineering, mines, etc., a drilling mud conditioner is used. The drilling mud conditioner is required to impart suitable lubricity to mud at the point where excavation blades are brought into contact with the ground for reducing the load to excavators and to impart high flowability to mud for readily discharging excavated chips by a pump. During discharging, when water in mud penetrates into the ground, then the flowability thereof would be greatly worsened, and therefore, it is also required to impart suitable water retentiveness to mud. For such purposes, as an additive to drilling mud, synthetic polymers such as acrylamide, etc., natural polysaccharides and their derivatives such as xanthan gum, carboxymethyl cellulose and others are used (for example, Patent Literatures 1 and 2).